This invention relates to torque wrenches, for example oilfield tubular torque wrenches.
When operating an oilfield tubular torque wrench (also known as a roughneck or a power tong), torque provided by a prime mover has to be applied to a tubular. Since tubulars do not feature any flat surfaces (such as a hex) around the circumference, the torque transfer from the wrench to the tubular has to be achieved through friction grip between the wrench's dies and the tubular itself. Since friction force is directly proportional to the coefficient of friction and the perpendicular (gripping) force, there is a strong correlation between the gripping force and maximum torque that can be transferred from the dies to the tubular.
Conventional oilfield tubular torque wrenches rely on hydraulic pressure to grip the tubular. In such designs, the gripping force applied is independent in operation from the torque being applied, i.e., the two are independently controlled. As such, it is possible to apply high torque while having relatively low gripping force which can lead to the dies slipping around the tubular and damaging it.
Some oilfield tubular torque wrenches rely on cam profiles to grip the tubular. In such designs, a pre-designed correlation exists between the torque and gripping force applied thus providing virtually slip-free operation. However, wrenches typically have limited gripping stroke which necessitates changing out the dies every time the diameter of the tubular changes.
Improved torque wrenches that address at least some of the foregoing problems are desirable.